3. Wireless Networks

Project Summary

Over past 8 years, I have worked on a number of different aspects of wireless communication.  The following project summary describes the current interest. 

Video streaming is now the major component of the peak hour real-time entertainment tra.c in the Internet for both wired and mobile access. Consequently, the user-perceived quality-of-experience (QoE) of video streaming applications is very important to the content providers to generate revenue. The growth of video streaming is also important to the network provider for capacity planning, provisioning and resource allocation both in the access and the backhaul networks. The QoE is determined by many factors such as startup delay, video freezes due to re-bu.ering, and the playback video bitrate. These depend on the dynamic network conditions including congestion in network and the time varying quality of the wireless channel. This research focuses on video streaming over LTE. One of the key problems in video streaming is the client-side bitrate adaptation (generically referred to as Adaptive Bit Rate (ABR)). These algorithms operate at the applications layer and modify the video bitrate on feedback from the client. In rate-based approaches, the video bit rate is selected to match highest possible bitrate based on the estimated available bandwidth. On the the other hand, in the bu.er based approach, the bu.er occupancy is used to select the video bit rate. While preliminary work have investigated the applicability of these approaches, there are many open questions including 1) how existing approaches perform under broadband multiaccess wireless networks such as LTE and how they can be optimized and 2) what are appropriate content-aware cross-layer design of ABR for LTE. 
As a fi.rst step we will carry out detailed performance analysis of dynamic adaptive streaming over HTTP (DASH) over LTE. Other than ABR and TCP control loops in DASH, there are additional control loops in the LTE radio access network. These including the RLC-AM which attempts to provide a near reliable delivery of data across the radio link and the MAC scheduler which allocates radio resources at a very fine time scale to achieve certain network-wide objective such a proportional fairness or maximum system throughput. Using an enhanced NS-3 based LTE simulation tool, we will study how the various control loops interact and the performance of DASH under di.fferent scenarios and the impact of the scheduler. We will study how the parameter of the growth and steady state phases in DASH should be set to maximize video quality.  An alternative to application layer ABR is to consider a cross-layer design in which the ABR control is tightly integrated with the MAC scheduler. We will build upon our preliminary work and design and implement a content aware cross-layer DASH for LTE. The intuition is that the since network itself would be the .rst to know about a congestion and variations in the channel quality, integrating the ABR control loop with the MAC scheduler will enable the servers and the clients adapt faster and more accurately, thereby providing better quality and maximize the network resource usage. This will require two-way information exchange - network provider passing information to the ABR control loop of the content provider and the content provider providing video content information to the network provider . While this sharing of information is easily conceivable in a IPTV "walled garden" environment such is not the case for majority of video streaming that is video "over the top". We will consider a multi-agent multiple control loop formulation of the problem to determine under what scenario is such information sharing is feasible and what are the benefits. 


Yu Liu
Ahmed Ahmedin 
Haiping Liu 
Xiaoling Qiu
Vishwanath Ramamurthi
Amitabha Ghosh